The present application relates generally to fuse accessories. More particularly, the present application relates to fuse state indicator modules for fusible disconnect devices.
Fuses are widely used as overcurrent protection devices to prevent costly damage to electrical circuits. Fuse terminals typically form an electrical connection between an electrical power source and an electrical component or a combination of components arranged in an electrical circuit. One or more fusible links or elements, or a fuse element assembly, is connected between the fuse terminals, so that when electrical current through the fuse exceeds a predetermined limit, the fusible elements melt, or otherwise fail, and opens one or more circuits through the fuse to prevent electrical component damage.
In some applications, fuses are employed not only to provide fused electrical connections but also for connection and disconnection, or switching, purposes to complete or break an electrical connection or connections. As such, an electrical circuit is completed or broken through conductive portions of the fuse, thereby energizing or de-energizing the associated circuitry. Typically, the fuse is housed in a fuse holder having terminals that are electrically coupled to desired circuitry. When conductive portions of the fuse, such as fuse blades, terminals, or ferrules, are engaged to the fuse holder terminals, an electrical circuit is completed through the fuse, and when conductive portions of the fuse are disengaged from the fuse holder terminals, the electrical circuit through the fuse is broken. Therefore, by coupling and decoupling the fuse to and from the fuse holder terminals, a fused disconnect switch is realized.
Known fused disconnects are subject to a number of problems in use. For example, any attempt to remove the fuse while the fuses are energized and under load may result in hazardous conditions because dangerous arcing may occur between the fuses and the fuse holder terminals. Some fuseholders designed to accommodate, for example. UL (Underwriters Laboratories) Class CC fuses and IEC (International Electrotechnical Commission) 10×38 fuses that are commonly used in industrial control devices include permanently mounted auxiliary contacts and associated rotary cams and switches to provide early-break and late-make voltage and current connections through the fuses when the fuses are pulled from fuse clips in a protective housing. In some instances, the protective housing may have a drawer for receiving the fuses, and one or more of the fuses may be pulled from the fuse clips, for example, by removing the drawer from the protective housing. Early-break and late-make connections are commonly employed, for example, in motor control applications. While early-break and late-make connections may increase the safety of such devices to users when installing and removing fuses, such features increase costs, complicate assembly of the fuseholder, and are undesirable for switching purposes.
Structurally, the early-break and late-make connections can be intricate and may not withstand repeated use for switching purposes. In addition, when opening and closing the drawer to disconnect or reconnect circuitry, the drawer may be inadvertently left in a partly opened or partly closed position. In either case, the fuses in the drawer may not be completely engaged to the fuse terminals, thereby compromising the electrical connection and rendering the fuseholder susceptible to unintended opening and closing of the circuit. Especially in environments subject to vibration, the fuses may be jarred loose from the clips. Still further, a partially opened drawer protruding from the fuseholder may interfere with workspace around the fuseholder. Workers may unintentionally bump into the opened drawers, and perhaps unintentionally close the drawer and re-energize the circuit.
Fusible switching disconnect devices and modules, as described in U.S. application Ser. No. 11/674,880, have been developed that may overcome the aforementioned difficulties. Fusible switching disconnect devices have been developed that may be switched on and off in a convenient and safe manner without interfering with workspace around the device; may reliably switch a circuit on and off in a cost effective manner and may be used with standardized equipment in, for example, industrial control applications; and may be provided with various mounting and connection options for versatility in the field. However, these devices can only be used with a battery powered ICM and therefore are not compliant with the Deutsches Institut für Normung (DIN) 43880 standard that governs the size of devices and accessories.